OP, look in the Suspension/Brakes/Chassis section of this forum:
http://www.e90post.com/forums/forumdisplay.php?f=38
for lots of discussion on how to improve the ride quality of M-Sport/RFT set-ups. Cheapest solution seems to be:
1) Ditch the runflats for normal tyres
2) Fit Koni FSD dampers.
Hope that helps.